The present invention relates to a dust filtering and collection system, and more particularly, to a dust filtering and collection system for use in mobile vacuum loading/unloading vehicles or other industrial environments, and to a dust filtering system employing hollow polymer tubes suspended within a dust filtering and collection canister or chamber.
Pneumatic conveying systems are widely employed for transporting free flowing material, i.e., starch, flour, Kaolin clay, soda ash, hydrate lime, plastic pellets, etc., from a railcar to a hopper truck, from a hopper truck or railcar to storage, or from storage to a railcar or hopper truck. In all such examples, the pneumatic conveying system employed may include a a vacuum driven system, a pressure driven system or a combination vacuum/pressure driven system.
In any of the aforementioned pneumatic conveying systems, heavier product particles are transported between locations as desired; however, lighter particles are captured in the moving air stream, and thus become part of a dust laden air stream. Where bulk products are transported from a railcar to a hopper truck, for example, dust laden air is generated within the storage chamber of the hopper truck, and then is transported as a dust laden air stream in the air flow return path of the pneumatic conveying system.
To alleviate the build up of the incoming dust laden air stream, dust filtering systems have been employed in the air flow return path, for cleaning and removing dust particles from the dust laden air stream, in order to provide a dust cleansed air stream which can then be exhausted back into the storage chamber. Typically, such dust filtering systems are of the dry bag type in which a series of juxtaposed, elongated air bags made of woven textiles or porous cloth materials are employed in the dust filtering and collection canister or chamber for removing dust particles from the dust laden air stream. Examples of such dust filtering systems which include dry air bags are shown in U.S. Pat. Nos.: 3,480,330; 4,017,281; 4,264,345; 4,433,987; 4,435,197; and 4,452,617. In lieu of woven textile or porous cloth fabrics, some dry bags have been of pleated paper tubes, as disclosed, for example, in U.S. Pat. No. 4,007,026. There have even been some welded or seamed filter tubes made from polymer or plastic material in some types of dust filtering systems.
In all of the aforementioned examples employing fabric (textiles or paper) bag or tube constructions, the life cycle of the fabric bags or tubes is very limited, not only because of the filtering operation itself, because the fabric bags or tubes are subjected to vigorous movement back and forth relative to one another in the canister or chamber, causing the fabric bags or tubes to come into contact with one another and other structural elements within the canister or chamber. In addition, the manner in which the fabric bags or tubes are suspended within the canister or chamber does not provide a structurally supported and sealed arrangement which enhances long life. Furthermore, cleaning of the fabric bags or tubes is required, generally after each loading or unloading operation, and in some cases even several times during the loading/unloading operation. As can be appreciated, all of the above circumstances can substantially limit the life cycle of the fabric bags or tubes in the dust filtering system.
Another problem in using dust filtering systems is that after the dust is filtered from the dust laden air stream, the accumulated product particles, formed from the collected dust particles, are simply thrown away. For example, in a mobile vacuum loading/unloading hopper truck, as disclosed, for example, in U.S. Pat. No. 4,227,993 where cyclone separators are employed, and in other dust filtering systems, such as U.S. Pat. No. 3,480,330, a valve below the canister or chamber in the dust filtering system is typically opened and the collected dust particles, are then simply dumped into a box or other container and thrown away. When removed from the self-contained pneumatic conveying system, the accumulated product particles are considered to be contaminated, and so they are simply thrown away as waste. In some cases, up to 500 pounds of accumulated product particles, filtered off by the dust filtering system, are thrown away as contaminated products. As will be appreciated, the product waste in current dust filtering systems cannot be economically justified, if there was any possible way of re-claiming or re-cycling the accumulated product particles back into a storage chamber from which the dust laden air stream emanates.